Oxide ceramics are strong and resistant to both creep and oxidation at high temperatures. However, for many applications, they are brittle and susceptible to thermal shock failure. On the other hand, metals, which are ductile and less prone to thermal shock failure are susceptible to destructive oxidation at high temperatures. A combination of the desirable qualities of ceramics with those of metals has led to materials called cermets, from combining and contracting the words ceramic and metal.
Technology in ceramic-metal systems can be divided into two general areas. One area is classical cermet technology where metals are incorporated with ceramics in the form of powder, grains or granules, or by molten infiltration or by powder metallurgy techniques followed by suitable heat treatment.
A second area is the in-situ reduction of metal oxides or metal salts in and on the ceramic to form the metal. Widespread application for this area has been in the art of supported catalysts and catalysis.
Generally the term cermet is used to describe a ceramic matrix material having metallic particles dispersed in the ceramic body. The term is also used to describe the reverse, that is, a metal matrix having dispersed therein refractory or ceramic materials which impart ceramic-like characteristics to the cermet. Cermets are known in the art and have been described in the patent literature.
The background art has taught a mixture of metal fibers in ceramics which can be a physical mixture or formed by the reduction of a mixture of ceramic and metal oxide in a reducing atmosphere. Representative patents teaching such mixtures include U.S. Pat. Nos. 4,397,963; 4,147,911; 3,560,408; and 3,321,285.
The background art also taught a ceramic coated with a metal or the hydrogen reduction of a ceramic coated with metal oxide, including fibers, to give refractories having a variety of uses as in, for example, U.S. Pat. Nos. 4,525,387; 4,327,131; 4,234,338; and 3,460,971.